在 .Net 中分层异步/等待

Question

Given an application where I want to do some asynchronous execution of code does it matter that I have multiple layers of async/await methods?

Let's take for example a web application (using asp .net core).

We have a controller that does something simple like:

public class MyController : Controller
{
    private readonly MyDbContext _context;

    public MyController(MyDbContext context)
    {
       _context = context
    }

    public async Task<ActionResult> GetResource()
    {
       var resources = await _dbContext.Resources.ToList();
       return Ok(resources);
    }
}

If I added a seperate layer of abstraction (let's say for example I'm using a repository pattern):

public class MyController : Controller
{
    private readonly MyRepository _repo;

    public MyController(MyRepository repo)
    {
       _repo = repo
    }

    public async Task<ActionResult> GetResource()
    {
       var resources = await _repo.GetResources();
       return Ok(resources);
    }
}

public class MyRepository 
{

    private readonly MyDbContext _context;

    public MyRepository(MyDbContext context)
    {
        _context = context;
    }

    public async Task<Resource> GetResources()
    {
        return await _context.Resources.ToList();
    } 
}

Note I'm very much aware that I could do the code underneath, but am trying to illustrate a point.

    public Task<Resource> GetResources()
    {
        return _context.Resources.ToList();
    }

All though this may be a contrived example because awaits will be ripped out when it gets to the bytecode.

From my understanding the run time will create a thread when it reaches an await so will it in the first example create one thread, and in the second create two threads.

With this in mind is it better to keep any asynchronous tasks as close to the entry point as possible?

Answer 1

does it matter that I have multiple layers of async/await methods?

No. It is normal to go async all the way .

The proper way to think about it is that your I/O operations are naturally asynchronous. Eg, database queries. So anything that calls those are also naturally asynchronous. Eg, domain or logic layer. So anything that calls those are also naturally asynchronous. Eg, controller. You don't start at the controller and "make it asynchronous"; you start at the I/O and make it asynchronous. Controller methods that don't do I/O shouldn't be asynchronous.